Method for coating an ophthalmic lens within an injection molding machine

ABSTRACT

A method for in-mold coating of an injection molded thermoplastic lens that resides in an injection molding machine oriented to a horizontal parting line. An optical lens is initially formed by injecting molten thermoplastic resin into an edge-gated lens-forming cavity held closed under a primary clamp force. The mold is opened at a time when the lens is rigid enough to retain its shape. An unpressurized full metered charge of coating is applied onto the center of the lens. The coating is co-molded by ramping up the clamp force from zero to a secondary clamp force less than the primary clamp force to compress the coating into a uniformly thick, fringe-free layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to manufacturing in-situ coated thermoplasticlens, by applying a coating solution to the surface of ophthalmic lenswhile it is still in the mold.

2. The Prior Art

In-situ coating via a direct injection process, so called in-moldcoating was originally developed to improve the surface appearance offiber reinforced thermosetting composites such as SMC and BMC parts. Inrelatively more recent years it's been applied to injection moldedthermoplastic parts.

For the regular injection molding process, the thermoplastic piece isejected out of the mold once it is rigid enough to resist thedeformation caused by ejection. In-situ coating injection integrateswith injection molding by injecting thermoset coating liquid on theexterior surface of the thermoplastic piece when the thermoplastic pieceis solidified to the degree that it won't be damaged by the coatinginjection. More coating is injected after the desired surface coverageis obtained to achieve certain coating thickness.

This method of in-mold coating has an advantage, in that the coating isable to cure at the same time as the part is cooling. Since access tothe part is limited, most of these systems introduce the coating at thetop of the mold cavity with the coating injector being located near theparting line. Generally, the molding machine configurations having avertical parting line, with the movable mold half being reciprocated ina horizontal direction. An example of such machine configuration can bereadily seen in U.S. Pat. No. 6,180,043. This patent is concerned withhigh gloss, opaque coatings, containing as much as 30% and up to 45%titanium dioxide and other pigments. Clearly, for such coatings in whichone sees only a highly reflective outer surface, there is no requirementfor uniformity or transparency, as with an optical coating.

In patents and publications such as: U.S. Pat. No. 6,676,877, WO2004/048068, US 2003/0077425, 2003/0082344 (corresponding toInternational Publication WO 03/035354) and US 2003/0099809, a method ofin-mold coating without opening the mold is disclosed. Several speciallydesigned features of the mold such as coating containment shroud weredescribed. These features can prevent coating solution fromcontaminating the liquid resin in the nozzle and the barrel of theinjection molding machine or leaking from the parting line. However,since coating is injected into a no-gap cavity filled withthermoplastic, a high coating injection pressure is required. Inaddition, there is no requirement for coating thickness uniformity ortransparency, as with an optical coating.

U.S. Pat. No. 5,943,957 discloses a method for pad printing inked imagesonto injection-molded pieces while they are still in the mold. Thepatented method relates to conventional ink that air dries, and does notinvolve an optical grade coating that will be spread over the lens byre-clamping the mold inserts and allowing the coating to cure via theretained heat in the mold block. Published U.S. Patent Application2003/0152693 discloses pad printing of lenses, but applies a UV ormicrowave curable coating on cast lenses which are totally divorced fromany contact with an injection molding machine.

The present invention provides a method to apply coating on the surfaceof ophthalmic lens while it is still in the mold. Coating is thermallycured by the heat from the mold and the residual heat from thethermoplastic lens.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an in-mold coatingsystem that results in a coating of optical quality.

It is a further object of the present invention to apply the coatingsolution in an unpressurized state to the lens while the mold is open.

It is another object of the invention to co-mold the coating into auniformly thick, fringe-free layer.

This application discloses a simple method of in-mold applying coatingon the ophthalmic lens by taking advantage of a horizontally-orientedparting line in which the mold opens and closes vertically. In general,the method includes injecting molten thermoplastic resin into anedge-gated lens-forming cavity held closed under a primary clamp force.Opening the mold at a time when the lens is rigid enough to retain itsshape and depositing an unpressurized full metered charge of coatingonto the center of the lens. Then we co-mold the coating by ramping upthe clamp force from zero to a secondary clamp force less than theprimary clamp force to compress the coating into a uniformly thick,fringe-free layer. The co-molding step includes reclamping the open moldto the same cavity volume to spread the coating radially-outwardly to alens periphery within a surficial zone. During said reclamping step, thecoating is spread in the absence back pressure. The coating is co-moldedto exactly replicate the part-forming surface without deforming thelens.

The depositing step includes applying a liquid coating in an open-airstate that thermally cures from the heat of the solidifying lens and themold and forms an optically transparent coating. The mold utilizes aprimary clamp force in the range of 100-150 tons and opens and closesvertically. The secondary clamp force is in the range from about 10% toabout 90% of the primary clamp force. The secondary clamp force may beless than, or equal to, the primary clamp force. The full metered chargeof coating is between 0.1 ml and 0.8 ml, and more specifically between0.2 ml and 0.5 ml.

The coating may be applied to polymethyl(meth)acrylate, polycarbonate,polycarbonate/polyester blends, polyamide, polyester, cyclic olefincopolymers, polyurethane, polysulfone and combinations thereof.Excellent results have been achieved with polycarbonate derivatives. Theliquid coating includes at least one mono-, di-, multi-, orhexafunctional (meth)acrylate compounds, a catalyst, and a metal salt.The catalyst is selected from alkyl aralkyl peracide compounds. Themetal salt may be cobalt naphthenate. The liquid coating has a reactedkick-off temperature near the molding temperature of the substrate lens.

During the co-molding step, the coating is cured for about 2 minutes to5 minutes. The edge-gated lens-forming cavity is one of an afocal lensforming cavity, a unifocal lens forming cavity, a bifocal straight-toplens forming cavity, a trifocal straight-top lens forming cavity, and aprogressive lens forming cavity. The latter stage of co-molding includesejecting the lens from the mold after the coating has cured and the lensis capable of withstanding ejection forces without deforming. The moldmay be reopened to apply additional layers of the same or a differentcoating. Such coatings may include photochromic coatings, anti-fogcoatings, anti-static coatings, anti-scratch coatings, protectivecoatings, anti-reflective coatings, clear coatings, cosmetically tintedcoatings and anti-smudge coatings. The invention further coversthermoplastic ophthalmic lenses manufactured by the described methods.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages, nature, and various additional features of the inventionwill appear more fully upon consideration of the illustrativeembodiments now to be described in detail in connection withaccompanying drawings. In the drawings wherein like reference numeralsdenote similar components throughout the views:

FIGS. 1A and 1B are graphs showing clamping force as a function of timefor two different prior art coating systems.

FIG. 1C is a comparative graph illustrating an embodiment of the coatingsystem according to the invention.

FIG. 2 is a schematic, perspective view of the coating system equipmentaccording to an embodiment the invention.

FIG. 3 is a flowchart showing various steps according to an embodimentof the coating method according to the invention.

FIG. 4 is a graph similar to FIG. 1C with the steps from FIG. 3 addedthereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Thermoplastic lenses must be extremely clean before they can be coated.In the regular lens coating process, after the lenses are taken out ofmold and degated, they have to be transferred and go through severaldifferent cleaning tanks before being coated. The coatings often requireheat or UV light in order to cure. The transfer, cleaning, coating andcuring operations utilize vast amounts of space and have high powerdemands to operate conveyors, pumps, heaters and curing ovens. That addsto the cost of the finished product. Accordingly, it would be desirableto coat a lens soon after it is formed by injection molding. In contrastto the prior art, a lens can be coated within 10-20 seconds of initialenvironmental contact before ejection or degating, thereby eliminatingthose operations as contamination sources.

The prior art coating methods disclosed in WO 03/031138 and U.S. Pat.No. 6,180,043 employ additional coating injection systems to pumpcoating into the mold cavity after the substrates are formed. To adaptthe mold used in the regular injection molding processes to theprocesses in above two references, besides the additional coatingcontainment designs or shear edge structure to reduce or eliminatecoating leakage, molds have to be modified in order to accommodate thecoating injector. For single cavity injection of large automotive parts,it is possible to mount a single injector on top of the injectionmolding machine. It would be very difficult and costly to handlerelatively small multi-cavity lens molds by using above methods. In asix cavity mold, the lowest cavity has the runner exiting from the top,effectively interfering with the placement of a coating injectordirectly above the mold. Also, variations of the clamp pressure afterinjection of the coating, as disclosed in U.S. Pat. No. 6,180,043significantly increase the process complexity. Accordingly, it issurprising that the method according to the invention calls for coatingthe lenses in a much simpler and more cost efficient way than either ofthe references mentioned here.

An embodiment of the lens coating process according to the inventionwill be characterized by the following steps. In the cooling stage ofthe lens molding, the mold will open for coating deposition. The moldcan open as soon as the lens substrate is rigid enough to sustain moldopening. That is, the lens shape which determines the degree ofaberration and power, will resist deformation under molddepressurization and vacuum forces. The coating is deposited as anunpressurized coating solution onto the lens substrate. The mold isreclamped to contact the coating with the upper mold insert and spreadan even layer over the lens surface. The coating spread pressure isdirected in exactly the same direction and manner as the lens formingclamp pressure. Once closed the coating is heated from below with lenssubstrate, and from above with mold insert. A 2-4 minute coating curephase is provided while the lens achieves sufficient solidification tobe ejected from injection molding machine.

Referring now in detail to the figures and in particular, FIG. 1A, thereis shown a schematic graph of a prior art method of clamping force F_(C)versus time, from U.S. Pat. No. 6,180,043. After the initial ramp up,the resin is injected at point IR. Once the automotive part has achievedsolidification capable of withstanding a coating pressure and coatingflow pressure the clamp force F_(C) is ramped down to about 5-10 tons orless, as stated in the examples. The coating is driven by the injectionpressure, that is positive pressure +P, at point IC, to spread out overthe surface of the part. The clamping force is then increased beforeundergoing a multistage, variable clamp force reduction. This clampforce profile helps minimize deformation on structural ribs of theautomobile parts being coated with pigmented coatings.

Referring now to FIG. 1B a further example of a prior art method showinga constant clamping force that is employed throughout almost the wholein-mold coating process. This graph represents the process from WO03/031138, as can best be understood. Again, the coating is driven bythe injection pressure, that is positive pressure +P, at point IC, tospread out over the surface of the part.

The comparative graph of FIG. 1C illustrates the coating application atpoint AC, at zero pressure, 0P, according to the invention The methoddoes not balance an injection pressure with clamp force. On the clamforce F_(c) axis, we show an opening of the mold, represented in dottedline below the zero F_(c) axis. This is not representing a negativeclamp force, but rather schematically illustrating where on the timeaxis the mold opening (at zero clamp force) occurs. A much lowerclamping force, compared to that applied during lens molding, is appliedto reclamp the mold after the coating injection. By using the insert tospread the coating under clamping force, there is almost no possibilitythat the coating spreading process will deform the shape or surface ofthe lens and a uniform coating thickness can be achieved.

In general, the methods according to the invention will utilize astandard injection molding machine that has a horizontal parting linewith the movable clamp plate on top. The machine can be hydraulic,electric or hybrid machine. A coating dispenser is provided adjacent tothe mold and is adapted to pivot or extend into the open mold.

As can be seen in FIG. 2, we orient the fixed or stationary mold half 10on the bottom, with the movable mold half 12 on top, and capable ofvertical clamping motion via an electric or hydraulic clamping unit 14.Clamping unit 14 can provide 100 tons or more clamping force as istypical in optical lens molding. Between the mold halves lies ahorizontally oriented parting line 16. The mold halves are equipped witha runner system 18. A resin screw injector 20 is aligned with the inputof runner system 18. Portions of runner system 18 may be located in thefacing surface of movable mold half 12.

A screw-jack 30, or similar height adjusting device supports alens-forming insert 32 within a receiver 34. Circulating channels 36 maybe located within the receiver, or nearby in the mold block, which havea temperature control fluid circulated therethrough by a thermolator 38.Screw injector is also heated to melt the resin. In the case ofpolycarbonate, the screw injector may have a heating range of 500 to 600degrees F. Thermolator 38 may heat receiver 34 to a range of 200 to 300degrees F. Similar temperature control lines may be located withinmovable mold half 12.

A process controller 50 is coupled to clamping unit 14, resin injector20, thermolator 38 and other components to coordinate the molding oflenses as is known in the art. According to an embodiment of theinvention we further provide a coating applicator 60 which is coupled tocontroller 50. More specifically, coating applicator 60 is mountedadjacent the mold halves for pivoting, sliding or other reciprocatingmotion to position applicator heads 60 a over the lens cavities orlenses. For example, applicator 60 is bracketed to the side of lower,stationary mold half 10. An arm 60 b, shown as a T-shaped arm, isequipped with a rack 60 c that is driven by a pinion 60 d. Uponactuation by controller 50, pinion 60 d drives arm 60 b in a directionparallel to plane 16, into the open mold to position heads 60 a over thejust injected lens mass. A full metered charge or drop of coating 60 e,fis deposited onto each lens L1, L2 to be coated. Arm 60 b may pivot,swing or follow another path to bring it into the position shown in thedrawing. One head may be employed to sequentially apply coating ontoeach lens. For 4-, 6- or 8-cavity molds (or more) additional heads orsequential applications may be employed. It is axiomatic, that moreheads will reduce cycle time by simultaneously applying a coating andretracting to close the mold sooner. The retracted position is shown indotted line to the left of arm 60 b.

According to the invention, the lens molding process will include thefollowing steps. After injection (and any packing phase) the mold willopen. The coating is deposited as an unpressurized coating solution ontothe center of the round lens. The mold is reclamped to contact thecoating with the upper mold insert and spread it into an even layer overthe lens surface. The coating spread pressure is applied in exactly thesame direction and manner as the lens forming clamp force. The coatingis heated from below by the lens, and from above by the upper moldinsert. A 2 minute minimum coating cure phase occurs while the lensachieves sufficient solidification to be ejected from injection moldingmachine.

As can be seen in reference to FIGS. 2 and 3 and 4, a conventional cycleinitiation is commenced with the closing of the mold, in step 100,injecting resin (IR) 102 and optionally applying packing pressure 104.During this injection stage, a primary clamp force, of about 100 tons ormore is utilized. Once the lens is rigid enough to sustain mold opening,the mold is opened, in step 106. Mold opening constitutes upwardvertical retraction of the movable side of the mold. Arm 60 b isadvanced, and the coating is applied 108. For example, for lenses of allpowers and configurations, the coating may be applied onto, or near, thecenter of the lens. The lenses will all generally have a circular outerperimeter. After arm 60 b is retracted, movable mold half 12 closes tospread the coating across the entire upper lens surface 110. The coatingis spread radially outwardly from the center, or near the center, of thelens, out to the circular periphery. During the co-molding stage 112, asecondary clamp force, less than the primary clamp force is utilized.Once the secondary clamp force is achieved, it may remain constant untilthe ejection stage is initiated. After the coating is cured, and thelens has solidified sufficiently, the mold is opened 114, and the coatedand cured lens is ejected 116.

For the multi-pair cavity molds, the invention covers two or more pairof lens cavities fed by a corresponding number of runners. The runnersextend radially outwardly from a central source that is coupled to theresin screw. The radially-extending runners lie in a horizontal plane. Alens forming cavity is disposed at the outer terminal end of eachrunner. In one embodiment, the coating applicator has four heads thatare positioned -in the same spaced relationship as the lens formingcavities. The applicator arm extends into the open mold to a locationwhere each head resides directly over a lens that is located within eachpart-forming cavity. Coating is simultaneously drop fed, at zeropressure, onto the center of each lens. The heads may be retained by anapplicator arm having a double T shape, square/rectangular shape,diamond shape or X shape. For molding 3 pairs, 4 pairs or more lenses,the applicator arm may have circular shape or a spider shape with acentral hub and 6, 8 or more legs extending radially out from thecentral hub. One reservoir of coating solution may be provided tomultiple applicators. Each applicator may have its own reservoir ofcoating solution. In an advanced coating system, it may be desirable toapply two different coatings, by repeating steps 106-112 after the firstcoating has cured sufficiently to receive a second coating. There may beprovided two, or more, central reservoirs of coating, feeding one or twoapplicator heads per lens. Each lens may alternately have twocorresponding reservoirs which feed one or two separate applicatorheads.

More particularly, the methods to manufacture in-mold coatedthermoplastic lens comprises the steps of:

-   -   a. conduct the regular injection molding cycle to mold        thermoplastic lens first    -   b. at end of the lens molding cycle, open the mold while without        ejecting the lens, so the lens sits still in the cavity in the        way that convex surface facing upward. Depends on which surface        of the lens is to be coated, the lens can also be molded in the        way with concave surface facing upward.    -   c. deposit coating liquid in the center of the lens convex (or        concave) surface.    -   d. reclamp the mold right after the coating deposition by moving        the upper mold half downward. Coating was compressed by the        clamping tonnage and spread out to cover the whole convex (or        concave) lens surface. Coating is thermally cured by the heat        from the mold plates and the residual heat in the lens        substrate. Coating thickness depends on the shrinkage and        compressibility of the lens substrate.    -   e. after 2 to 5minutes, reopen the mold and eject the coated        lens

The substrate that could be used in this method could be any injectionmoldable lens material like PMMA, polycarbonate, polycarbonate/polyesterblend, polyamide, polyurethane, polysulfone, cyclic olefin co-polymers,etc. In a preferred embodiment the substrate is polycarbonate.

The injection cycle is as usual and depends from the nature of thethermoplastic. Usually the mold temperature is comprised from 240° F. to290° F., the melt temperature is comprised from 540° F. to 600° F., thepacking pressure is comprised from 5000 psi to 15000 psi, the packingtime is comprised from 10 sec to 50 sec, and the cooling time iscomprised from 60 sec to 265 sec.

EXAMPLE 1

First, a 6 base 10 mm thick PC lens was injection molded on an injectionmolding machine of which the mold is of horizontally oriented partingline. The top mold insert is a concave insert which will form the lensfront surface and the bottom mold insert is a convex insert will formthe lens back surface. The main molding parameters consisted of moldtemperature set at 270° F., melt temperature ranging from 550° F. to560° F., packing pressure set at 10950 psi for 45 seconds and coolingdown for 255 seconds.

At the end of the molding cycle, the mold opened for coating deposition.Without removing the lens from the cavity a thermal curable coating,0.25 ml was deposited in the center of the injected lens, using anauto-dispenser. The mold was re-clamped and held for 3 minutes at 270°F.

Finally, the mold was opened and the optically clear, fringe-free coatedlens was ejected from the mold insert.

Following is the coating composition that was used in the example.

COMPONENT CONCENTRATION (%) Ebecryl 5129 50.0 Ebecryl 284N 26.0 Hydroxypropylmethacrylate 15.28 Isobornyl Acrylate 7.6 t-butyl perbenzoate 1.0Cobalt Naphtenate 0.1 Surfactant EFK 3034 0.02

A coating according to the present invention advantageously providesand/or includes at least the following characteristics:

-   -   the coating is solvent free; in fact no volatile organic        compounds (VOCs) should be generated during the in-mold coating        process, which could perturb the polymerization parameters and        thus the optical property of the lens;    -   the coating is cured at a thermoplastic substrate high molding        temperature while maintaining its optical clarity without        etching the thermoplastic substrate;    -   the coating can flow across the front surface of the lens before        it gels and fast cures thereafter; the kinetic parameters are        important to improve flow characteristics;    -   the coating, advantageously, will impart desirable functional        properties onto an ophthalmic lens such as, tintability, scratch        resistance, etc.

A coating according to the present invention is thermally curable,optically clear, does not show visible interference fringes aftercoating onto a lens and comprises an optically transparent coating thatis compatible with the lens material in order to adhere to it withoutcausing any undesirable effects while imparting the desired features(tint, scratch resistance, etc.) onto the lens material.

A coating composition according to the present invention is preferablysolvent less and includes an acrylate compound. The acrylate compound ispreferably thermally cured, which means the coating may be cured via,e.g., azo, peroxides, and/or blocked tertiary amine. Chemicallyspeaking, the coating composition preferably includes multi-functionalacrylates comprising up to hexa functional groups and with variousmolecular weights. Preferably, the present invention comprises amulti-functional urethane acrylic coating that is modified to meetvarious competing requirements. For example, such coating needs to stayin liquid form to flow along a hot mold insert to an even thickness andthen polymerize rather quickly, since the lens molding process is beingextended by the coating set time. Indeed, a coating used in the presentinvention advantageously remains in liquid form to flow along a heatedmold insert to a uniform thickness and then polymerizes quickly.

More particularly, a coating composition according to the presentinvention preferably comprises acrylates including monofunctionalacrylates and/or monofunctional methacrylates such as isobomyl acrylateand hydroxylpropyl methacrylate, as well as tetrafunctional acrylatesand/or tetrafunctional methacrylates and hexafunctional acrylates and/orhexafunctional methacrylates. Exemplary acrylates that may be used inthe present invention may include and are not limited to reactivemultifunctional acrylates, preferably hexafunctional aliphatic urethaneacrylates. For example, exemplary acrylates used in the presentinvention may include hexafunctional acrylates and at least onedifunctional acrylate. As noted herein, the term “(meth) acrylate”refers to either the corresponding acrylate or methacrylate.

Acrylates may be obtained from UCB Chemicals or from Sartomer and Henkel(a German Co.), and may in one embodiment comprise, e.g., Ebecryl™ brandacrylates. A brief general description of various Ebecryl acrylates inEB number formats which may be used according to the present inventionis as follows:

-   -   1) 284: aliphatic urethane diacrylate diluted 12% with HDOHA.        Excellent light fastness, exterior durability, toughness and        good flexibility.    -   2) 1290: hexafunctional aliphatic urethane acrylate containing        an acrylated polyol diluent. Provides fast cure with excellent        hardness, solvent and abrasion resistance.    -   3) 5129: hexafunctional aliphatic urethane acrylate combining        good scratch resistance with improved flexibility    -   4) 8301: hexafunctional aliphatic urethane acrylate containing        an acrylated polyol diluent.

Use of hydroxylpropyl methacrylate presents a particular interest toslow down the reaction in the coating composition. Multi-functionalacrylates of three functional groups or higher advantageously willprovide more cross linking and result in higher abrasion resistance. Forexample, hexa-functional acrylates will provide a high degree of crosslinking due to having six (6) functional groups. The urethane backboneof these high functional acrylates provides flexibility and greaterability to resist heat. Difunctional acrylate species are used toincrease the flexibility and toughness and to control the viscosity ofthe formulation for process-ability to a certain extent.

A monofunctional methacrylate, such as hydroxylpropyl methacrylate,serves as a monofunctional diluent and kinetic modifier. It is used toterminate the reaction or to slow down the propagation of polymerizationso that it will have some stability and a window of reactivity forprocessing. Monofunctional methacrylates used in a composition accordingto the present invention serve as reactive diluents and kineticmodifiers to improve flow characteristics.

With regards to the term acrylates, it is to be noted that methacrylatesand other unsaturated compounds, whether mono- or multifunctional mayalso be used in addition to, or instead of, acrylates. In some casesmethacrylates may experience a slower chemical reaction duringpolymerization. Acrylate or methacrylate compounds may be selected fromthe family of aliphatic urethane acrylates which include, e.g., from twoto about six functional groups.

In a preferred embodiment of the present invention, high molecularweight acrylates (for example, acrylates having a molecular weight of atleast 1000 centipoises (cps) or higher at 25° C.) are preferably usedfor ophthalmic injection molding according to the present invention.This embodiment presents the advantage of improved control of theviscosity and flow of the coating composition on a heated surface. Forexample, a high injection pressure requires a high viscosity flow toallow for the higher temperature (i.e., higher than room temperature)during applied extrusion. It is to be noted that the viscosity mayfurther be adjusted as necessary based on the particular injectionmolding parameters and requirements.

In one embodiment of the present invention, the coating compositionpreferably comprises an acrylic base cured with an initiator (e.g.,t-butyl perbenzoate). In fact, the thermal cure process of the presentinvention utilizes free radical polymerization. The initiator (t-butylperbenzoate) obtains energy by absorbing heat to decompose and generatefree radicals (that is, the free radical reaction is generated bythermal heating). These free radicals then attach monomers or oligomers(reactive multifunctional acrylates) to generate more free radicals topropagate the reaction to form long molecular chains and eventually across-linked network.

An in-mold coating composition according to the present inventionpreferably may further include at least one catalyst (initiator) and atleast one metal salt. The catalyst may be selected from, e.g., alkylaralkyl peracide, azo derivatives and blocked tertiary amine, ispreferably selected from ketone peroxides, diacyl peroxides,dialkylperoxides, diperoxyketals and peroxyesters, and in a verypreferred embodiment comprises tert-butylperbenzoate.

The examples disclosed herein preferably use peroxides derived fromalkyl aralkyl peracide with a metal salt promoter. Peroxides are used tocure the coating via a free radical reaction. Metal salt promoters helpto generate free radicals quickly and minimize oxygen inhibition. Themetal salt and peroxide concentration are preferably chosen to fit acuring cycle for the current process. The concentration ratio can bevaried as necessary to fit a particular process requirement. Again,although use of peroxides for curing is a preferred method, and morespecifically tert-butyl perbenzoate is a preferred candidate,alternative methods for curing may include use of azo and blockedtertiary amine.

The metal salt is preferentially selected from cobalt naphthenate,cobalt octoate, cobalt neodecanoate, copper naphthenate, zincnaphthenate, and potassium octoate, and preferably, the metal saltcomprises cobalt naphthenate.

In one embodiment, an exemplary coating composition according to thepresent invention comprises the following: (a) at least onehexafunctional acrylate and/or hexafunctional methacrylate compound; (b)at least one difunctional acrylate and/or a difunctional methacrylatecompound; (c) Hydroxyl propylmethacrylate; (d) Isobomyl acrylate; (e)T-butyl perbenzoate; and (f) Cobalt naphthenate.

An in-mold coating composition according the invention may optionallyfurther include a surfactant which is preferably selected from afluorinated surfactant or a silicone surfactant. That is, a surfactantsuch as a fluorinated surfactant (e.g., EFKA 3034) or a siliconesurfactant (e.g., Silwet L-7602) may be included in a coatingcomposition according to the present invention. The surfactant in thecoating composition may be added to improve wetability of the moldsurface.

The coating composition may also optionally include acrylic or epoxyfunctionalized colloids, for example, OG-101 or OG-103 (available fromClariant), or functionalized colloidal silica with acrylic silanes, orother colloids such as, e.g., cerium colloid, niobium colloid, andantimony colloid.

An in-mold coating composition according to the present invention mayfurther optionally include, e.g., a metal alkoxide which may beselected, for example, from zirconium isopropoxydes, methyltrimethoxysilane and tetraethoxysilane.

A coating composition according to the present invention may furtheroptionally include at least one dichroic dye, a photochromic dye and/orone liquid crystal.

It is to be understood by one of ordinary skill in the art that thecoating should preferably retain its qualities at the lens substratemolding temperature, e.g., for a polycarbonate substrate, suchtemperature is around 250° F.

Upon coating of an optical lens, a coating according to the presentinvention is optically clear and may have a thickness ranging from about1 micron to about 100 microns. For example, typical abrasion resistancecoating thickness ranges from about 1 micron to about 8 microns, and aphotochromic system can be up to about 20 microns or more.

Advantageously, an in-mold coating composition according to the presentinvention provides very good anti-abrasion properties. To furtherincrease abrasion resistance, it is also possible to include in thecoating formulation according to the present invention acrylic or epoxyfunctionalized colloids, as discussed above. Metal alkoxides and itsderivatives may also optionally be added as discussed above to increaserefractive index, abrasion resistance and perhaps influence the rate ofpolymerization.

According to one embodiment, a coating composition according to thepresent invention comprises the following:

Hexafunctional aliphatic range: about 33% to 52% preferred: 50% urethaneacrylate Aliphatic urethane diac- range: about 13% to 31% preferred:25.6% rylate diluted 12% with HDOHA Isobornyl acrylate range: about 6%to 9% preferred: 7.6% Hydroxylpropyl methac- range: about 12% to 18%preferred: 15.4% rylate Tetrabutylperoxybenzoate range: about 0.5% to 2%preferred: 1% Metal complex (e.g., range: about 0.25 to 1% preferred:0.4% cobalt naphthenate)

EXAMPLE 2

The insert in the top mold half is a concave insert that is ofstraight-top structure, in order to make bi-focal lens. All the moldingprocedures and coating formulations in use were the same as in Example1.

When the mold firstly opened, prior to coating deposition, it wasobserved that straight-top structure was very well replicated in thelens front surface. After the coating curing and mold reopen, theoptically clear, fringe-free coated bi-focal lens was ejected from themold. The straight-top structure was also very well retained in both thecoating layer and the lens substrate.

Optical grade coatings are difficult to achieve with straight-topstructures, including bi-focal and tri-focal lenses. The surfacediscontinuity in the vicinity of the straight-top interferes withcoating on to, and flow off-of, the lens surface, that negativelyimpacts conventional spin-coating and dip-coating techniques. Theinvention utilizes the part-forming surface to compress the coating/lensensemble in a manner which “molds” the exterior surface of the coating,to form a coating layer of uniform thickness.

This example demonstrates an important feature of the invention, whichis referred to as “co-molding.” We define co-molding as a process inwhich the mold in reclamped onto the coating drop with the clamp forcethen ramping up from zero to a secondary clamp force. The secondaryclamp force may remain constant once it has reached its maximum value.The maximum value may be less than, or equal to, the primary clamp forceemployed to mold the lens. In other words, the secondary clamp force isnot greater than the primary clamp force. Under the secondary clampforce the coating is conjointly molded and compressed with the lens.While co-molding is present in every embodiment of the invention, itsbenefits are most easily recognized in connection with discontinuouslens surfaces, like the straight-top bifocal described in this example2. Co-molding helps replicate the shape of the lens surface in thecoating. Co-molding uses the same fixed cavity volume at all times andcontains the coating with a surficial zone that results from resinshrinkage. This contributes to uniform coating thickness, which is animportant factor in producing optically clear coatings. One embodimentof the co-molding process is to maintain a constant secondary clampforce.

The inventive method coated straight top lenses just as successfully assmooth lenses. In comparative testing a straight top lens of 10 mmthickness and a smooth lens of 10 mm thickness were both coated with asecondary clamp force near the primary clamp force. The coatingthickness on the straight top was 20 μm+/−4 μm and for the smooth lens16 μm+/−4 μm. Although the thickness varied from lens to lens, each lenshad a coating with uniform thickness across its entire surface.Variations should be narrowed upon implementation of molds specificallydesigned to contain liquid coating solutions.

EXAMPLE 3

A 6 base 10 mm polycarbonate lens was injection molded first using thesame machine and same molding parameters as in example 1. Mold was thenopened and a liquid coating drop, 0.25 ml with blue dye in it, wasdeposited in the center of the lens front surface. The mold was thenreclamped to thermally cure the coating for 2 minutes. This correspondsto steps 100-112 on the flowchart of FIG. 3. The mold was then reopenedand another 0.25 ml coating drop without blue dye in it was deposited inthe center of the already coated lens front surface. The mold was thenreclamped for another 5 minutes to cure the coatings. This secondcoating application follows the path of step 120, wherein steps 106, 108and 110 are repeated. Finally, the mold was opened and the opticallyclear, fringe-free bi-layer coated lens was ejected from the mold.

In this example, the first full metered charge is 0.25 ml. The secondfull metered charge is 0.25 ml. In other words, all the coating for agiven layer, is deposited at one time, in a drop onto the center of thelens.

Alternatively, it is possible to apply different coatings, each with adifferent optical function to produce an in-mold multifunctional coatedlens. The multiple coating layers may be independently selected fromphotochromic coatings, anti-fog coatings, anti-static coatings,anti-scratch coatings, protective coatings, anti-reflective coatings,clear coatings, cosmetically tinted coatings and anti-smudge coatings.

An important aspect of the open mold coating application according tothe invention, is that in the initial phase of reclamping 110, thecoating is able to spread out at low, or no back pressure. For example,as the coating begins to spread upon contact with the upper lens insert,the parting line may still be open resulting in no back pressure. As themold closes further, the coating may continue to spread under very lowback pressure. Thus the coating covers the entire lens surface underrelaxed conditions, contributing to the fringe-free coated lens, evenupon application of two coating layers. This spreading condition, incombination with the co-molding process, leads to a uniformly thincoating layer, with very high optical quality, and reduces or eliminatesfringes on a variety of lens surface contours. Fringes are wavelikecontours in the coating layer which can cause distortion due to thevarying thickness from peak to trough.

In a comparative test, 2 mm thick lenses were coated with a secondaryclamp force that was about 40% of the primary clamp force. At 2 mmthick, the low volume of polycarbonate does not shrink much, leavingonly a paper thin surficial gap in the fixed volume cavity used duringprimary and co-mold clamping. Coating thickness was 3.9 μm+/−0.3 μm. atdouble the clamp force, the coating was uniformly 1.2 μm+/−0 μm thick.At the same clamp force, a 10 mm lens had a coating thickness of 16μm+/−4 μm.

Having described preferred embodiments for lens manufacturing, materialsused therein for coatings and methods for processing same (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments of the inventiondisclosed which are within the scope and spirit of the invention asoutlined by the appended claims. Having thus described the inventionwith the details and particularity required by the patent laws, what isclaimed and desired protected by Letters Patent is set forth in theappended claims.

1. A method for optically coating an injection molded thermoplastic lensthat resides in an injection molding machine oriented to a horizontalparting line, comprising the steps of: injecting molten thermoplasticresin into an edge-gated lens-forming cavity of an injection moldingmachine held closed under a primary clamp force; opening the mold at atime when the lens is rigid enough to retain its shape; depositing anunpressurized full metered charge of liquid coating onto the center ofthe lens; and co-molding the coating by ramping up the clamp force fromzero to a secondary clamp force not greater than the primary clamp forceto compress the liquid coating into a uniformly thick, fringe-free layerwithin the same lens-forming cavity volume, wherein the liquid coatingthermally cures from the heat of the solidifying lens and the injectionmold to form an optically transparent coating.
 2. The method of to claim1, wherein the co-molding step includes reclamping the open mold tospread the coating radially-outwardly to a lens periphery within asurficial zone.
 3. The method of to claim 2, wherein during saidreclamping step, the coating is spread in the absence back pressure. 4.The method of to claim 1, wherein the co-molding step includesco-molding the coating to exactly replicate the part-forming surfacewithout deforming the lens.
 5. The method of claim 1, wherein saiddepositing step comprises applying a liquid coating in an open-airstate.
 6. The method according to claim 5, wherein the liquid coatingincludes one or more (meth)acrylate compounds, a catalyst, and a metalsalt.
 7. The method according to claim 6, wherein the liquid coatingincludes at least one hexafunctional acrylate compound, at least onedifunctional acrylate compound, and at least one monofunctional acrylatecompound.
 8. The method according to claim 6, wherein the catalyst isselected from alkyl aralkyl peracide compounds.
 9. The method accordingto claim 6, wherein the metal salt is Cobalt naphthenate.
 10. The methodaccording to claim 5, wherein the liquid coating has a reacted kick-offtemperature near the molding temperature of the substrate lens.
 11. Themethod of claim 1, wherein the mold opens and closes vertically.
 12. Themethod of claim 1, wherein the primary clamp force is over 100 tons. 13.The method of claim 12, wherein the secondary clamp force is in therange from about 10% to about 90% of the primary clamp force.
 14. Themethod of claim 1, wherein the primary clamp force is about 150 tons.15. The method according to claim 1, wherein the full metered charge ofcoating is between 0.1 ml and 0.8 ml.
 16. The method according to claim1, wherein the full metered charge of coating is between 0.2 ml and 0.5ml.
 17. The method according to claim 1, wherein the thermoplastic resinis selected from the group consisting of polymethyl(meth)acrylate,polycarbonate, polycarbonate/polyester blends, polyamide, polyester,cyclic olefin copolymers, polyurethane, polysulfone and combinationsthereof.
 18. The method according to claim 17, wherein thermoplastic isa polycarbonate derivative.
 19. The method according to claim 1, whereinsaid co-molding step includes curing the coating for about 2 minutes to5 minutes.
 20. The method of claim 1, wherein the edge-gatedlens-forming cavity is one of an afocal lens forming cavity, a unifocallens forming cavity, a bifocal straight-top lens forming cavity, atrifocal straight-top lens forming cavity, and a progressive lensforming cavity.
 21. The method of claim 1, wherein following saidco-molding step, the method further including the step of: ejecting thelens from the mold after the coating has cured and the lens is capableof withstanding ejection forces without deforming.
 22. The method ofclaim 1, wherein following said co-molding step, the method additionallyincluding the step of: further opening the mold at a time when the lensis rigid enough to retain its shape; further depositing an unpressurizedfull metered charge of further coating onto the center of the lens; andfurther co-molding the coating by ramping up the clamp force from zeroto a secondary clamp force to compress the further coating into afurther uniformly thick, fringe-free layer.
 23. The method of claim 22,wherein the further deposited coating is the same as said depositedcoating.
 24. The method of claim 22, wherein the deposited coating isselected from the group consisting of photochromic coatings, anti-fogcoatings, anti-static coatings, anti-scratch coatings, protectivecoatings, anti-reflective coatings, clear coatings, cosmetically tintedcoatings and anti-smudge coatings.
 25. The method of claim 22, whereinthe further deposited coating is different from said deposited coating.26. The method of claim 25, wherein the further deposited coating has adifferent optical function from said deposited coating to produce anin-mold multifunctional coated lens.
 27. The method of claim 26, whereinthe deposited coating and the further deposited coating areindependently selected from the group consisting of photochromiccoatings, anti-fog coatings, anti-static coatings, anti-scratchcoatings, protective coatings, anti-reflective coatings, clear coatings,cosmetically tinted coatings and anti-smudge coatings.
 28. The method ofclaim 22, wherein said steps of further opening, further depositing andfurther co-molding are repeated for the application of a third or higherlayer of coatings.
 29. A thermoplastic ophthalmic lens manufactured bythe process of claim 1.